Web heating furnace



April 18, 1961 T. F. A. EDVAR WEB HEATING FURNACE Filed March 6, 1957 2 Sheets-Sheet 1 INVENTOR. TORSTEN F. A. EDVAR ATTORNEY.

April 18, 1961 'r. F. A. EDVAR WEB HEATING FURNACE 2 Sheefis-Sheet 2 Filed March 6, 1957 FIG. 2

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J nace.

United States Patent WEB HEATING FURNACE Filed Mar. 6, 1957, Ser. No. 644,331

3 Claims. (Cl. 263-3) The present invention relates to furnaces or ovens, and more particularly to a furnace wall construction that a very low heat storage capacity.

In the heating of web material, such as plastic film or thin sheet metal, for example, the web is pulled through a narrow furnace in front of suitable burners. When for some reason the web is stopped, the burners are cut 'off. If, however, the furnace has a large heat storage capacity, the web can still be damaged even though direct heat from the burners is stopped. This diificulty has in some cases been overcome by moving the furnace walls away from the web, or moving the web out of the furmovement of heavy equipment in order to avoid damage to or tearing of the web. 7

In accordance with the present invention the furnace walls are constructed of sheet material in such a way that the necessary furnace wall insulation is obtained by radiation. and re-radiation between the sheets. The sheets, however, are spaced from each other so that there isno heavy mass of material to absorb and retain heat. When the web being heated is stopped, the burners are turned off and air is drawn through the furnace and between the sheets forming the wall thereof. Thus the sheets, which cannot absorb much heat, are quickly cooled and damage to the web is prevented.

It is therefore an object of the invention to provide a furnace having a very low heat storage capacity. It is also an object of the invention to provide a furnace in which a web can be heated and one in which the web not be damaged if it is stopped in the furnace. An'

other object of the invention is to provide a means for quickly cooling a furnace chamber and the walls thereof when the heat is cut off.

The present invention is particularly adapted for the heating of web materials and will be so described. It will be obvious however that it is equally as well adapted for the heating of strands such as wire and thread.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects attained with its use, refrence should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of the invention. 7

In the drawings:

Fig. 1 is a section through the furnace taken on line 1-1 of Fig. 2.

Fig. 2 is a section of the furnace taken on line 2-2 of Fig. 1, and

Fig. 3 is a diagrammatic view of a control system.

The furnace as a whole comprises a pair of parallel walls 4 and 5 which face the surfaces of a web 6 that is being heat treated, and a pair of connecting end walls 7 and 8 that face the edges of the web 6. These walls form a narrow, vertically extending chamber 9 through which the web is moved. The furnace walls are mounted,

has

Both of these expedients require the accurate Patented Apr. 18, 1961 at their lower ends, on a frame 11 of structural steel and are rigidly supported in their vertical position by suitable braces 12. The lower end of the furnace is open while the upper end communicates with an exhaust chamber 13 that is connected at opposite ends with an exhaust duct 14.

' The side and end walls of the furnace are each formed of a series of parallel sheets 15 of metal such as stainless steel which are provided with highly reflecting surfaces. Between each of the sheets 15 is a vertically extending air space 16 that is open at its lower end and which communicates directly at its upper end with the exhaust chamber 13. As noted above the spaced metal sheets which form the walls of the furnace chamber are preferably made of some metal such as polished stainless steel. The outer layers of the wall or the outer sheets may, however, be made of some less expensive steel and covered with foil such as aluminum foil which has a highly reflective surface. The inner surfaces of walls 4 and 5 are provided with a series of rows of burners 17 that are connected, as shown in Fig. 2, in zig zag fashion extending across the width of the walls and substantially the height of the furnace chamber. Each of these burners is shown herein as being of the so-called radiant cup type similar ,to those disclosed in Hess Patent 2,215,079, granted September 17, 1940. Such burners are each provided with a cup shaped depression 18 and the various depressions are connected by channels 19. Each burner is supplied with fuel through a centrally located distribution member 21 that is attached to a manifold 22. The arrangement is such that the various burner blocks 17 are supported by the distributors 21 which in turn are fastened to the manifolds in side by side relation. Thusthere is provided a continuous row of burners across the face of the furnace wall. The manifolds are connected by suitable piping which is supplied with a combustible fuel mixture through a pipe 23. If desired, the inner sheet 15 of the furnace wall may be bent, as shown, so that its surface is flush with the manifolds 22. In operation the burners produce radiant heat that is directed toward opposite surfacesof the web. It will be obvious, of course, that any suitable type of burner may be used. A suitable burner will'be one in which the heat storage capacity of the burner itself is low enough so that the web will not be harmed when the burner is cut off.

The products of combustion produced by the burners rise through the furnace chamber into the exhaust cham ber 13 and exhaust duct 14. This duct is connected with a dual stack 24 that has one portion 25 connected with a stack for natural draft, and another portion 26 that is connected to a suitable source of reduced pressure such as a blower. Exhaust duct 14 is connected with stack 25 or with stack 25 by meansof a damper 27 that can be moved from the position shown in Figs. 2 and 3, in which duct 14 is connected with the natural draft stack 25 to a position to the left thereof, in which duct 14 is connected with the stack 26. The damper is pivoted at 28 and is provided with an arm 29 that is connected by a link 31 with a solenoid 32 which is used to pull the damper to the position shown. The damper is normally biased into its other position by means of a spring 33 that is also connected to the outer end of arm 29.

Referring to Fig. 3, there is shown diagrammatically the control system by means of which the damper is operated. In this figure there is also shown a normally closed solenoid valve 34 that is located in the fuel mixture line 23, and a motor 35 which is used to drive the web moving mechanism which carries web 6 through the ,and,-through suitable connections in the starter 36, sole noid valve 34 and solenoid 32 are also energized. The

damper zjj to" a 'positi'o'n in which the exhaustldnct-fis connected with natural draft stack '25. "'As 'th'i'slti'm'e throughsome co'nventional'apparatus that is not'shown such a" spark ignit'er coopera'ting with one of the cups 7 18, the burners are ignited. Due to the channels 19 extending between each of the burner cups one cup will 7 be flash ignited-by the next adjacent thereto and light ing of thelburn'ers'will progress through" the various rows point in the burner ro w'so that'th'e ignition will take place towardoppos'ite" ends and therefore reduce the time required to light all the burners. During this time chamber, with guide rollers 37 above and below the furnace toguide'the 'web ina straight path through the webwillbe heatedwill depend upon the'speed with which the web is pulled through the furnace chamber.- This can thereof until all ofthem ar'e'ignited; It is noted tha t the spark ignition: is preferably placed at or nearthe midthe'web is being" moved by motor 36 through the furnace T combustion is used to heat the web,ior to heat treat it for 7 some particular purpose. The temperature to which the be varied, however, for a given speed by varying the num- H 7 her of burners or rows of burners that are supplied with fuel, as well as the pressure of the fuel supply.

During the'time that the burners are in operation the products of combustion will rise in the chamber to duct 1 4 and will escapethrough stack 25, at the'sa'me time 7 V is radiaed between sheets '15. These currents will also rise and pass' through the stack. When the drive motor for the web is-stopped, solenoid valve 34 and solenoid 32 will be de-energzed. This will cut; off the: supply of fuel andwill permit spring 33 to move damper 27-to a posi- ,tiori in which exhaust duct 14 is connected with stack 26;

Since this stack is under a reduced pressure, cool air will bedr'awn in through" the bottom of the furnace up through the furnace chamber, as well asgth'rough the air hecreflected back toward that chamber. The various air spaces and reflecting surfaces of e the furnace walls have a high degree of insulating value so that no great amount jof heat will be lost through them from the furnace.

'- In addition, due to the reflecting surfa'ce of the sheets and. the fact that they have a relatively small mass, there will not be muchiheatstorage capacity. Therefore the walls of the furnace can be cooled quickly b'y the air flowing over and between them to stack 26. These walls can be 'co'oledidown so rapidly that no harm is done to the web that remains in the furnace, eventhough'it is thin and delicate. r

convection currents will be created in spaces 16 as heat Thusthere is provided by :Lthisinvention a furnace construction in which the walls have a good heat insulatingvalue but have a negligible amount of'heat storage capacity. The construction is light and is easily assembled. Furthermore; 'a'construction'of this: type can be made of readily available sheet metal with a minimum of special shaping and fitting of the parts. The arrangement is such'th'at as soorrasthe web is stopped, or ifthere should be a failure of ower, the furnace is immediatelycooled down'in order to protect the webs While in accordance with the provisions of the statutes, I have illustrated andldescribed the best form of embodiment of my inventiofi ino'w known 'ton'fle, it will be apparent to those. skille'diii the arttha't; changes may be made in the form of theapparatus disclosed without departing from the spirit and scope of the invention set forth in the appended claims, and that in some cases certainieatures ofmy invention maybe used to advantage without a corresponding. use "of: other features. 2

Whatisclaimedis: I I 1' 11" i l. In combination, Istructureforming a'furnace having a chamber therein, burners in said" chamber; a first'stack for natural =draft'-connected to Tsaid' furnace, "a: second stack connected to 'a source of reduced :pressurera damp 'er operative tofconneet said chamberfto' oneor the other of said staclr's, means normally to operatesaid damper to connectsa'id chamber to said secon'd stack, a fuel supply pipe having a normally closed valve therein,*:and: means operable simultneonsly to-. open: said valve andiadjust said damper to connectsaid chamber with. said first "stack;

'2.-'The'eombination oft'claim sl including means t move a web of material to' be heated through said cham ber, and mechanism responsive to operation of said;

located along said walls} means to' supply fuel to: said burners including a nor mally closed valve, a firstrstack for nat ural l l'rafti in communication-with the upper ends ofsaid furnace,-a second stack connected with a source of reduced-pressure also-in communication with the upper end of said chamber, damper means.;movable between positions inwhich: it connects' Jsaid first or said second stack with's'aid chamber and having a normal. position in which saidsecond stack isi'conneetedtherewith, and means operable simultaneously" to open said'valveand move said damper to connect said 'first stack and said chamber. 4

References Cited the patent r r UNITEDVVSTAITESIP'ATENTS 1,992,620 Johnson 1. "Feb'. 26, 1935 2,210,032, Hess; Aug. 6; 1940 2, 6 ,987; Hess et al Jan. 6, 1942 2,328,078 7 Ku'gler Aug; 3 1, 1943 2,404,060 ,Hall1etal.'.. July16 1946 2,4 4, 9 "Ofien V V an; 28, 1947 '2',47 6,916. .Roseet a1. -2 July,19,2194 9 2,641,205: 'Dolezal .June9, 1953 FOREIGN PATENTS I 115,264 Sweden Oct. 30,1945 

